The use of granular adsorbent materials for gas filtration has been known for a long time. Adsorbent materials are used for this purpose as so-called bulk bed filters in a housing.
The drawback of these bulk bed filters is that the adsorbent particles are packed densely, which leads to a relatively high pressure drop during the flow of the gas through them, especially if finer granular adsorbent materials are used. An additional drawback of bulk bed filters arises from the fact that the filter housing, which usually imitates simple geometric shapes, such as cylinders or parallelepipeds, has a preset geometry for manufacturing technical reasons. To avoid the drawbacks of bulk bed filters, it is therefore desirable to have a possibility of adjusting the packing density of the adsorbent packing as needed, on the one hand, and, on the other hand, to generate a structure of the gas filter media that can be flexibly adapted to different geometries corresponding to the intended use or the site of use. It has been known in this connection that shaped adsorbent structures can be formed by mixing adsorbent particles with an adhesive and a subsequent exposure to temperature and subsequent shaping. The drawback of such structures is that their packing density is relatively high and it comes rather close to that of bulk bed filters, so that the pressure drops associated with it are too high for some applications. On the other hand, to obtain filter structures with especially low pressures drops, it was suggested that support structures, which have only a low air resistance, be provided with adsorbent particles by means of suitable adhesives. The adsorbent structures thus obtained have the drawback that besides the adsorbent particles and the adhesive, which are the indispensable components, they also contain the support structure, which is undesirable for cost reasons and is disadvantageous for the overall efficiency of the filter material.
Thus, a layered filter mat for kitchen range hoods has become known from EP 00 69 323 A1. A granular filter layer consisting of activated carbon or the like is introduced there between porous and flexible cover webs, preferably nonwoven fabrics, and is connected to the cover webs by means of an adhesive.